1. Field of the Invention
The present invention relates to an optical transceiver for transmitting and receiving an optical signal.
The present application claims priority based on Japanese Patent Application No. 2008-230978, filed in Japan on Sep. 9, 2008, the content of which is incorporated herein by reference.
2. Description of Related Art
Normally, optical transceivers include a transmitter optical sub-assembly (TOSA) for receiving an electric signal to convert into an optical signal and a receiver optical sub-assembly (ROSA) for receiving an optical signal to convert into an electric signal, a LD driver for generating an electric signal to the TOSA, a circuit board mounted with a limiter amplifier or the like for amplifying an electric signal from the ROSA, and a flexible substrate connecting the TOSA and the ROSA with the circuit board (for example refer to Japanese Laid-Open Patent Application No. 2007-043496).
The TOSA and the ROSA are assembled products in which a laser diode (LD), which is a light-emitting element, or a photo diode (PD), which is light-receiving element, and other parts are integrated. Such assembled product is called an optical sub-assembly (OSA).
The flexible substrate has high-speed signal lines for transmitting an electric signal between the TOSA or the ROSA and the circuit board, other lines other than the high-speed signals such as power supply lines for supplying power to the TOSA or the ROSA, and a ground layer.
Recently, signal transmission speed in optical communication is improving. Also, with the improvement in signal transmission speed, there is an increase in the frequency of electric signals transmitted by the high speed signal lines of an optical transceiver. However, there is the problem that unnecessary high-frequency current generated when a semiconductor element or the like supplies a high-frequency signal to a high-speed signal line or the unnecessary high-frequency current generated as a result of resonance or the like by reflection in impedance mismatching places of the high-speed signal line flows into other lines such as a power supply line, becoming high-frequency conduction noise, which has an adverse effect on high-frequency signals or the like transmitted by high-speed signal lines.